1. Field of the Invention
The present invention relates to the design of digital networks. More specifically, the present invention relates to a method and system for discovering network paths which include both layer-2 and layer-3 switches.
2. Related Art
Hi-performance web sites often rely on “server farms”—hundreds of networked computers performing similar tasks—for scalability, reliability, and fast response time. Deploying these server farms typically requires the power of a high-speed, versatile network to provide reliable connectivity and sufficient bandwidth among the servers.
Conventionally, servers are interconnected through IP routers which process packets on layer-3, or the IP layer. By processing every packet's IP header based on routing tables, IP routers provide flexibility and re-configurability. However, such heavy processing also imposes constraints on router speed. Consequently, high-speed ports on an IP router are expensive, and building an entire server-farm network using only IP routers can be very costly.
One way to lower network costs is to combine the versatility of IP routers with the inexpensive high bandwidth available in layer-2 switches. Layer-2 switches require less per-packet processing and, hence, can provide high-speed ports at a lower cost. The most widely deployed layer-2 switch is the Ethernet switch, which forwards Ethernet frames based on layer-2 forwarding tables. Moreover, the recently ratified standard for 10-Gigabit Ethernet (10 GbE) further unleashes the power of fiber-optic transmission and allows high-speed Ethernet switches to inter-operate with a wide range of legacy equipment. Other proprietary layer-2 or sub-layer-2 protocols facilitate the construction of large-scale, high-speed Ethernet switch fabrics. A typical topology of such a network includes layer-3 switches located at the “edge” of the network, providing access connectivity to the servers, and layer-2 or sub-layer-2 switches located in the “core,” providing high-speed inter-connectivity to the layer-3 switches.
During a network's operation, maintaining accurate knowledge of the network state is critically important for reliable service provisioning. Hence, a network operator needs effective tools to monitor the network state and the health of each switch. In a conventional IP network, one can identify the route from a source to a destination using the traceroute command, which returns the IP address and response time of each IP router along the path. In a multi-tier network with layer-3, layer-2, and sub-layer-2 switches, however, the traceroute command becomes insufficient, because the switches operating below layer-3 are “invisible” to the traceroute command.
Hence, what is needed is a method and a system that facilitates discovery of switching devices on layer-3 and lower layers along a network path.